Swan bathtaps

[bullethead123]

Hi All,
Do 'swan' bathtaps have different backnuts to other brands? I couldn't get the old taps off with my trusty crow's foot basin wrench so i compared it to the new (exact same taps) and it's the wrong size.
Am I missing something here?
Chris

 

[terryplumb]

Although the thread is 3/4 bsp ,the back nuts do vary ,the measurement across the flats that is.